There a numerous methods to ornament, decorate and label articles. For example, decoration can be added to an article by molding, printing, painting, applying a decal, embossing, etching, engraving, among others. Printing, painting and decals are effective for creating flat, two-dimensional images, whereas, molding embossing, etching, and engraving can create textured, three-dimensional images.
The textured, three-dimensional images are often desirable because their visual appearance can change depending on the angle at which they are viewed and the angle of incident light. These images are commonly associated with more expensive, luxury articles. Indeed, decorating an article by molding, embossing, etching and engraving is usually much more expensive than decorating by most available printing techniques. Also, it is generally relatively expensive to change the decorative design created by these processes.
Guilloche is a centuries old form of engraving which is used to create the ornamentation on the dials that distinguish some of the most expensive and rare watches. The term guilloche is derived from the French word “Guillochis,” used to describe the mechanical creation of precise, regular decorative patterns comprising straight and rounded lines using a technique related to engraving. The engraving is performed by an artisan utilizing a rose engine (named for the shape of its cams). The engine is similar to a lathe but is hand powered. The decorated piece is fixed onto the engine. A cutting tool is held in place as the decorated piece is moved against the cutting tool. With one hand, the artisan cranks the engine to rotate the decorated piece while his other hand regulates the pressure of the tool against the decorated piece. FIG. 1 shows several examples of patterns created by the guilloche process. As one might imagine, decorating by guilloche is a time consuming, expensive process. Engraving a single watch dial can take a guillocheur an entire day, which a brocading machine, a type of pantograph, can produce a similar engraving in forty minutes. In order to produce similar looking dials for mass production quantities, most dials displaying guilloche like patterns are embossed or stamped. But stamped patterns do not reflect light in the same manner as an authentic guilloche engraved pattern.
Another design used to decorate articles which can produce the effect of a three dimensional image is a holographic image. Basically, a hologram is a recording of an interference fringe pattern between two beams of coherent light (typically light produced by a laser). The resulting recording is a series of very finely spaced lines of varying widths that acts as a diffraction pattern. When illuminated with only the reference beam or similar light, the object beam displaying the three-dimensional object image is reproduced in phase and amplitude.
For background, one process for producing a hologram will be explained with reference to FIG. 2. A laser is provided which produces coherent light, meaning light of the same wavelength and which is in phase. The laser light is split into two beams, a reference beam and an object beam, by a beam splitter. The reference beam is expanded by a lens or curved mirror and is aimed directly through an interference region onto a film plate. The film plate comprises a suitable high resolution photosensitive emulsion (e.g. silver halide) which can resolve over one-thousand spaced lines per millimeter (mm). The object beam is also expanded through a lens and is aimed at the three-dimensional object to be imaged. The object beam reflects off of the object and some of the reflected light reflects through the interference region. The reference beam and reflected object beam interact to form an interference pattern which is recorded on the film. One beam comprises light reflected from the object of which the image is being recorded and is called an “object beam.”
As described above, the resulting recording comprises a series of very finely spaced lines representing the interference pattern of the reference beam and reflected object beam. For typical wavelengths of visible light, the density of the lines is approximately 2000 lines per millimeter. Due to the very high resolution required, several precise processes have been developed for volume reproduction of the recorded holographic diffraction pattern. In one such process, photoresist is used to produce a metalized surface relief pattern on a master die. The master die is then used to emboss the diffraction pattern into a thermoplastic film which has typically been softened by heat, pressure, solvents or some combination thereof. In the last step, the film is coated with a highly reflective metal, such as aluminum or silver, usually by vacuum deposition. The result is a hologram in which the recorded light pattern is reconstructed in ordinary light reflected off the reflective metal coating and diffracted by the embossed diffraction pattern. The hologram can be attached to an article as decoration or as a product authentication device by lamination or other suitable attachment means. Several processes, including the one described above, for creating and replicating holograms are described in detail in U.S. Pat. Nos. 4,839,250, 5,882,770 and 6,017,657, the disclosures of which are hereby incorporated herein in their entireties.
Screen printing is another example of a useful technique for producing decoration and labeling on film substrates. Screen printing is also a very efficient and cost effective process for high volume, mass production of decorated and/or labeled articles. With its ability to vary and control ink thickness accurately, screen printing is an extremely versatile and useful process for decorating many different types of films which can then be applied to articles as decoration and/or labeling. While screen printing is generally well known to those skilled in the art, a short description will be included herein for completeness. Screen printing begins by creating the graphic design to be reproduced. Today, most designs are generated by computer with the aid of design drafting software, but the design may be created manually or by any other suitable method. The graphic design is then transferred onto a piece of clear film with the image printed in black. The black portions of the printed film prevent light from transmitting through the film. A screen mesh is coated with a light sensitive emulsion. The printed film is then fastened to the screen and exposed to a bright light. The dark areas of the film block the light from exposing the areas of the screen that are to print, and the transparent areas allow a photo-chemical reaction to harden the emulsion. When the screen is rinsed with water or other solvent, the emulsion washes out of the areas that were not exposed. This results in a screen with openings in the areas of the printed image. The screen is clamped into a frame that holds the screen steady during printing. The substrate to be printed is placed under the screen and is held by vacuum, clamps or other means during printing. With the screen lowered over the substrate and held at the correct off contact distance, ink is forced through the screen by the blade of a squeegee. The squeegee may be automated to control the speed, pressure, stroke and angle of the blade across the screen. Once the ink is printed onto the substrate it must be dried or cured depending on the type of ink. If the ink is solvent bases, then it may be dried by a gas or electric dryer. If the ink is curable, for example by exposure to ultraviolet (UV) light, then the printed substrate is exposed to ultraviolet light. Screen printing and processes for producing screens and stencils are described in greater detail in U.S. Pat. Nos. 6,634,289 and 6,539,856, the disclosures of which are hereby incorporated by reference herein in their entireties.
The decorated films created by the holographic and screen printing processes described above may be applied to articles by many different methods. One method for adding decorative designs to thermoplastically molded articles is the in-mold decorating (IMD) process, sometimes referred to as in-mold labeling (IML), full surface decoration (FSD) or film insert molding. In a typical IMD process, the printed film is trimmed to the dimensions of the mold and/or formed into a three-dimensional shape that matches the shape of the mold cavity. The printed film is then placed into a mold and molten thermoplastic resin is injected into the mold behind and/or around the printed substrate. The result is a one-piece, permanently bonded article decorated by the printed film. The IMD process is described in detail in U.S. Pat. Nos. 6,623,677 and 6,117,384, the disclosures of which are hereby incorporated by re entireties.
Various methods of printing graphics on articles to provide a textured or “tactile” look have been previously described. Such methods have been described for use in printing images on articles such as advertising signs, brochures, greeting cards, packaging material, trading cards and the like. For example, U.S. Pat. No. 6,042,888, issued Mar. 28, 2000 to Sismanis et al. describes a print article and method for making the print article which has a design which projects above the surface of a substrate. The substrate is described as being opaque with a reflective, shiny first surface (the first surface is the surface facing the intended viewing side of the substrate and a second surface is the opposite surface). The projecting design is formed by a layer of thick ink printed on the first surface of a substrate. The thick ink layer has sufficient thickness so that the thickness of the ink is visible to an observer and also has a tactile feel for an observer, similar to an embossed effect.
U.S. Pat. No. 5,968,607, issued Oct. 19, 1999 to Lovison, describes a printed article and process similar to Sismanis et al., except that Lovison is directed to a higher throughput continuous roll substrate and process for printing on a continuous roll. Typical ink thicknesses for the printed products and processes disclosed in Sismanis et al. and Lovison are greater than 0.01 inches. Furthermore, the printed lines are widely spaced apart (shown to be at least 0.1 inches or more) so that the individual lines are easily resolved from each other from a typical viewing distance. Indeed, it would be infeasible with the printing processes disclosed in Sismanis et al. and Lovison to print lines that are 0.01 inches or thicker to print very thin lines at very high line densities because such lines would tend to bleed together.